Fluoride-containing ion exchange membranes and their applications in flow batteries

Abstract

The present invention belongs to the field of ion exchange membranes, and discloses a fluorine-containing ion exchange membrane and its application in a flow battery. The fluorine-containing ion exchange membrane has the following structure: where x is the proportion of the perfluorononeneoxybenzenesulfonic acid structural unit in the total polymerization degree of the polymer molecular chain, and the value range of x is: 0.5 ≤ x ≤ 0.9, and the average total polymerization degree of the polymer should be above 2000, and R is a perfluoroalkyl group. The polymer molecules constituting the ion exchange membrane of the present invention have a relatively short side chain structure, making the arrangement of the polymer molecules relatively regular. Therefore, the ion exchange membrane is endowed with good mechanical properties and high flow battery efficiency, and has excellent durability or corrosion resistance and other properties, and can replace the existing ion exchange membranes and be applied to the field of flow battery energy storage.

Description

Technical Field

[0001] The present invention relates to the field of ion exchange membranes, particularly fluorine-containing ion exchange membranes and their applications in flow batteries, suitable for ion exchange membranes used in flow batteries, especially ion exchange membranes used in vanadium batteries. Background Art

[0002] Ion exchange membranes used in flow batteries need to face the environment of strong acids, strong oxidants and chloride ions in the electrolyte. Therefore, high requirements are imposed on the corrosion resistance of ion exchange membranes. Currently, the main ion exchange membranes used in the field of flow batteries are perfluorosulfonic acid ion exchange membranes (such as the series produced by DuPont Company in the United States, etc.). This is because the fluorine atoms contained in the perfluorosulfonic acid ion exchange resin molecules have strong electronegativity, making the perfluorosulfonic acid ion exchange resin have high corrosion resistance. However, due to the complex synthesis process of perfluorosulfonic acid ion exchange resin and the high production cost, the price of perfluorosulfonic acid ion exchange membranes remains high, which greatly increases the manufacturing cost of flow battery stacks. At the same time, perfluorosulfonic acid ion exchange membranes were originally designed and developed as ion exchange membrane materials for the chlor-alkali industry and were not developed for the field of flow batteries. Therefore, there are still some problems in their applications in the field of flow batteries, such as poor ion selectivity resulting in the mutual mixing of positive and negative active substances, causing cross-contamination between the positive and negative electrodes or battery capacity imbalance; the molecular structure of common perfluorosulfonic acid ion exchange resins is as follows:

[0003]

[0004] The side chains of the molecular chains constituting the membrane are relatively long and have too strong hydrophilicity, resulting in relatively irregular arrangement of the molecular chains of the membrane and relatively poor mechanical properties. Therefore, developing ion exchange membrane materials with good ion selectivity, excellent corrosion resistance and excellent performance in flow batteries is the key research direction in this field. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the technical solution of the present invention is as follows:

[0006] A fluorine-containing ion exchange membrane having the following structure:

[0007]

[0008] where x is the proportion of the perfluorononenyloxybenzenesulfonic acid structural unit in the total polymerization degree of the polymer molecular chain, with 0.5 ≤ x ≤ 0.9, and the average total polymerization degree of the polymer should be above 2000; (Note: The polymerization degrees of each structural unit can be jointly determined by the molecular weight of the polymer and 19 the FNMR nuclear magnetic resonance spectroscopy data, which will not be elaborated here.)

[0009] R is a perfluoroalkyl group, preferably a perfluoromethyl (—CF3) group, a perfluoroethyl (—C2F5) group, and a perfluoropropyl (—C3F7) group.

[0010] Further, the polymer molecules constituting the ion exchange membrane are copolymerized from perfluorononeneoxybenzenesulfonic acid monomers and perfluoroalkyl vinyl ethers; or prepared by copolymerizing perfluorononeneoxysulfonyl chloride and perfluoroalkyl vinyl ethers to obtain a polymer, and then hydrolyzing the sulfonyl chloride groups under acidic conditions. It should be noted that the perfluoroalkyl vinyl ether monomer may be in a gaseous state or a gas-liquid mixture state at normal temperature and pressure. Therefore, when implementing the polymerization reaction, pressurized conditions should be preferably considered (the pressure is selected according to the properties of the perfluoroalkyl vinyl ether monomer used, preferably above 3.5 MPa), so that the perfluoroalkyl vinyl ether monomer is in a liquid state at the reaction temperature and is fully dissolved in the solvent of the polymerization reaction, ensuring that the perfluorononeneoxybenzenesulfonic acid (or acyl chloride) monomer and the perfluoroalkyl vinyl ether monomer are fully mixed and copolymerized.

[0011] Further, the fluorine-containing ion exchange membrane can be prepared by methods such as melt extrusion film forming method and solution casting method from the polymer molecules constituting the ion exchange membrane as described above, and no limitation is made here. Additionally, it should be noted that the selection of the film forming method of the ion exchange membrane selected in the present invention can be reasonably screened according to the molecular weight or degree of polymerization of the polymer molecules constituting the ion exchange membrane. Generally speaking, when the polymer molecular weight or degree of polymerization is low, its solubility in the solvent is relatively good, and it is more suitable to use the solution casting method to prepare the ion exchange membrane; if the polymer molecular weight or degree of polymerization is high, its solubility in the solvent is relatively poor, so it is not suitable to use the solution casting method to prepare the ion exchange membrane, and the melt extrusion film forming method can be selected. The above is common knowledge in the art and will not be elaborated here.

[0012] Another object of the present invention is to claim the application of the fluorine-containing ion exchange membrane in a flow battery, which can be applied to all vanadium flow battery systems and theoretically can also be used in other flow battery systems, and can improve the mechanical properties, flow battery efficiency, and durability of the membrane in the vanadium battery system.

[0013] The inventive concept of the present invention is as follows: By combining perfluorononeneoxybenzenesulfonic acid units with perfluoroalkyl vinyl ether units, the resulting molecule has a relatively shorter side chain and a relatively regular structure compared to the molecule of the perfluorosulfonic acid ion exchange membrane (Nafion membrane). (The perfluorosulfonic acid ion exchange resin is copolymerized from a perfluorosulfonic acid ether monomer with a side chain structure and a tetrafluoroethylene monomer without a branched chain, and its polymer structure has a relatively large degree of irregularity.) Theoretically speaking, the fluorine-containing ion exchange membrane described in the present invention has good crystallization properties, with closely and densely arranged molecules, which endows the membrane with good mechanical properties. At the same time, the relatively dense molecular structure enables the prepared membrane material to have the function of blocking and screening active substances with relatively large water and ion radii, but basically does not affect the conduction of hydrogen ions (protons) with relatively small ion radii, endowing the ion exchange membrane with good ion selectivity. On this basis, through the screening and optimization of the proportion of the perfluorononeneoxybenzenesulfonic acid units containing a sulfonic acid structure, a membrane material with excellent charge-discharge performance (including coulomb efficiency and voltage efficiency) for a flow battery is obtained. For the perfluoroalkyl vinyl ether units without an ion exchange group, their main function is to reduce the influence of the steric hindrance effect of the perfluoroalkyl group and the benzene ring in the perfluorononeneoxybenzenesulfonic acid units, reduce the polymerization hindrance of the monomers, and promote the smooth progress of the polymerization reaction. In addition, the perfluorinated structure on the main chain of the ion exchange membrane molecule and the stable benzene ring structure on the side chain ensure the chemical corrosion resistance and durability of the fluorine-containing ion exchange membrane described in the present invention.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] (1) The present invention provides a fluorine-containing ion exchange membrane with a completely new structural composition. The polymer molecules constituting the ion exchange membrane have a relatively short side chain structure, making the polymer molecules arranged relatively regularly, thus endowing the ion exchange membrane with good mechanical properties and a relatively high flow battery efficiency.

[0016] (2) The fluorine-containing ion exchange membrane prepared by the present invention has excellent durability or corrosion resistance and other properties, and can replace the existing ion exchange membranes and be applied in the field of flow battery energy storage. Detailed implementation manners

[0017] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments. However, the content of the present invention is not limited to the following several embodiments. The following embodiments describe in more detail the fluorine-containing ion exchange membrane in the present invention and its application in a flow battery, and these embodiments are given by way of illustration, but these embodiments do not limit the scope of the present invention. Unless otherwise specified, the experimental methods used in the present invention are conventional methods, and the experimental equipment, materials, reagents, etc. used can be purchased from chemical companies.

[0018] The thickness of the ion exchange membrane was measured with a digital display micrometer, and 50 values were measured at different positions for each sample to calculate the average value;

[0019] For the test of the tensile strength and elongation at break of the ion exchange membrane, refer to the standard GB / T 1040.3-2006 "Determination of Tensile Properties of Plastics - Part 3: Test Conditions for Films and Sheets". Cut the membrane into strips with a width of 10 mm and an initial distance between clamps of 50 mm, and conduct the experiment at a tensile rate of 200 mm / min;

[0020] In the embodiments of the present invention, a typical flow battery - a vanadium redox flow battery is taken as an example to evaluate the performance of the ion exchange membrane in a flow battery. The performance test conditions of the ion exchange membrane in a vanadium redox flow energy storage battery: Charge and discharge experiments were carried out under the condition of a current density of 80 mA / cm 2 Charge to 1.55 V and discharge to 1.00 V. Use the graphite carbon felt produced by Liaoyang Jingu Carbon Materials Co., Ltd. as the reaction electrode, and the effective working area of the electrode is 48 cm 2 , and the positive and negative electrode electrolytes are VO 2+ / VO2 + and V 2+ / V 3+ sulfuric acid solutions, and the battery operating temperature is 37 °C.

[0021] Example 1

[0022] The molecular structure of the ion exchange membrane consists of perfluorononeneoxybenzenesulfonic acid units and perfluoromethyl vinyl ether monomer structural units, with a total degree of polymerization of 2108. The proportion of perfluorononeneoxybenzenesulfonic acid units in the total degree of polymerization is 0.52, and an ion exchange membrane with a thickness of 50 μm was prepared by the solution casting method.

[0023] Example 2

[0024] The molecular structure of the ion exchange membrane consists of perfluorononeneoxybenzenesulfonic acid units and perfluoroethyl vinyl ether monomer structural units, with a total degree of polymerization of 2234. The proportion of perfluorononeneoxybenzenesulfonic acid units in the total degree of polymerization is 0.54, and an ion exchange membrane with a thickness of 50 μm was prepared by the solution casting method.

[0025] Example 3

[0026] The molecular structure of the ion exchange membrane consists of perfluorononeneoxybenzenesulfonic acid units and perfluoroisopropyl vinyl ether monomer structural units, with a total degree of polymerization of 2119. The proportion of perfluorononeneoxybenzenesulfonic acid units in the total degree of polymerization is 0.56, and an ion exchange membrane with a thickness of 50 μm was prepared by the solution casting method.

[0027] Example 4

[0028] The molecular structure of the ion exchange membrane consists of meta - perfluorononenyloxybenzenesulfonic acid units and perfluoroisopropyl vinyl ether monomer structural units. The total degree of polymerization is 8965, and the proportion of meta - perfluorononenyloxybenzenesulfonic acid units in the total degree of polymerization is 0.73. An ion exchange membrane with a thickness of 50 μm is prepared by the solution casting method.

[0029] Example 5

[0030] The molecular structure of the ion exchange membrane consists of meta - perfluorononenyloxybenzenesulfonic acid units and perfluoroisopropyl vinyl ether monomer structural units. The total degree of polymerization is 15362, and the proportion of meta - perfluorononenyloxybenzenesulfonic acid units in the total degree of polymerization is 0.90. An ion exchange membrane with a thickness of 50 μm is prepared by the melt extrusion method.

[0031] Example 6

[0032] The molecular structure of the ion exchange membrane consists of para - perfluorononenyloxybenzenesulfonic acid units and perfluoroisopropyl vinyl ether monomer structural units. The total degree of polymerization is 26531, and the proportion of para - perfluorononenyloxybenzenesulfonic acid units in the total degree of polymerization is 0.75. An ion exchange membrane with a thickness of 50 μm is prepared by the melt extrusion method.

[0033] Taking the all - vanadium redox flow battery as an example, the fluorine - containing ion exchange membranes prepared in Examples 1 - 6 of the present invention and the commercially available Nafion 212 ion exchange membrane were subjected to performance tests. The test results are shown in Table 1.

[0034] Table 1 Performance data of Examples 1 - 6 and the commercially available Nafion 212 ion exchange membrane

[0035]

[0036] As can be seen from Table 1, the ion exchange membrane prepared by the present invention has better tensile strength compared with the Nafion 212 membrane of the same thickness, that is, it has better mechanical properties. From the vanadium battery efficiency (coulombic efficiency and voltage efficiency), it can be seen that the ion exchange membrane prepared by the present invention has excellent ion selectivity and low membrane resistance. From the data of the number of cycles required for the voltage efficiency to decay by 2%, the ion exchange membrane prepared by the present invention has strong durability, and its durability can basically exceed that of the Nafion 212 perfluorosulfonic acid ion exchange membrane, fully demonstrating that the fluorine - containing ion exchange membrane prepared by the present invention has excellent durability and corrosion resistance. Therefore, the fluorine - containing ion exchange membrane prepared by the present invention has excellent mechanical properties, good battery efficiency, durability and corrosion resistance, and has broad application prospects.

[0037] The above are only the preferred specific embodiments of the present invention creation, but the protection scope of the present invention creation is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention creation, according to the technical solution and inventive concept of the present invention creation, making equivalent substitutions or changes, shall be covered by the protection scope of the present invention creation.

Claims

1. A fluorinated ion exchange membrane, characterized in that: Has the following structure: Wherein x is the ratio of the perfluorononenyloxybenzenesulfonic acid structural unit to the total polymerization degree of the polymer molecular chain, 0.5≤x≤0.9, and the average total polymerization degree of the polymer is above 2000, and R is a perfluoroalkyl group.

2. The fluorine-containing ion exchange membrane according to claim 1, characterized in that The perfluoroalkyl group is any one of a perfluoromethyl (—CF3) group, a perfluoroethyl (—C2F5) group, and a perfluoropropyl (—C3F7) group.

3. The fluorine-containing ion exchange membrane according to claim 1, characterized in that The polymer is prepared by copolymerizing perfluorononeneoxybenzenesulfonic acid monomer and perfluoroalkyl vinyl ether.

4. The fluorine-containing ion exchange membrane according to claim 1, characterized in that The polymer is prepared by copolymerizing perfluorononenyloxybenzenesulfonyl chloride and perfluoroalkyl vinyl ether to obtain a polymer, and then hydrolyzing the sulfonyl chloride group under acidic conditions.

5. The fluorine-containing ion exchange membrane according to claim 3 or 4, characterized in that The pressure during the polymerization reaction of the polymer is above 3.5 MPa.

6. The fluorine-containing ion exchange membrane according to claim 1, characterized in that The polymer is prepared by a film-forming method or a solution casting method.

7. The use of the fluorine-containing ion exchange membrane according to claim 1, characterized in that: Applied in flow battery systems.

8. The use of the fluorine-containing ion exchange membrane according to claim 1, characterized in that: Applied in vanadium flow battery system.

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